You might have been told to "stay behind the ball" to really smash it. The goal being to support the hit with your whole body, like a boxer throwing a punch. But when you try to stay back, you end up hitting shots with your weight on your back foot. You'll have a hard time compressing the ball if you don't transfer to your front foot on the downswing.
Instead of trying to keep your upper body back, a few simple adjustments will help you accomplish that and still shift toward the target. First, address the ball with a slight tilt in your shoulders so your spine is angled away from the target. Your left shoulder should be higher than your right (above, left). Also, flare out your left foot a little. This will help you make a powerful body rotation through the shot.
But before you start rotating your hips on the downswing, shift them toward the target a few inches—this should actually start happening before you finish swinging the club back. This blend of lateral and rotary motion is the only way to shift forward correctly and have the power of your body behind the shot (above, right). Do this, and you've got the secret to great ball-striking.